Record number of vehicles fail MOT due to emissions

Over 1.27 million vehicles failed the MOT across the UK last year because of faults relating to exhaust emissions, new research suggests.

A Freedom of Information (FOI) request to the DVSA found more cars have failed on emissions in the last two years than any other before it.

Diesel vehicles have seen the greatest surge in failures due to emissions, with a huge rise of 240 per cent compared to just 37 per cent for petrol vehicles.

Although diesels have seen a much larger failure rate increase in recent years, petrol cars are actually still more likely to fail, with 4.5 per cent of the total number licenced failing annually due to emissions, compared to 3.3 per cent for diesels.

This means that exhaust emissions account for 7.8 per cent of all MOT failures in the UK.

Here in Ireland, a spokesperson from Applus+, the company that operates the NCT services, told us that the number of vehicles failing the national car test here due to exhaust emissions is “so small”, that it “doesn’t even make the top 20 defects list”.

Across in the UK, overall failures last year were up by more than 70 per cent compared to 2017/18 levels – the final year before the new regulations were introduced, according to, who tabled the FOI to the DVSA.

Class 4 annual MOT failures due to an emissions related fault
*New MOT regulations introduced from 20th May 2018

In May 2018, the UK government introduced tougher MOT regulations to clamp down on vehicles producing excessive emissions which led to a significant rise in failures.

“The regulations have mostly impacted diesel cars, causing more than triple the number to fail, compared to petrol car failures which have only increased by a third,” said Jessica Potts, head of marketing at

The large increase in diesel failures was caused by a change to rules for cars equipped with a diesel particulate filter (DPF). Any car equipped with a DPF will fail an MOT if there is either evidence it has been tampered with or if smoke of any colour can be seen coming from the exhaust.

DPFs became standard on all diesel cars in 2009 to comply with Euro 5 emissions standards, though a few cars older than this may also be equipped with a DPF. Its purpose is to trap soot particles from exhaust emissions which are toxic to humans.

DVSA also introduced new fault categories, with ‘Major’ or ‘Dangerous’ faults resulting in a failed test.

Almost all petrol emissions failures were classed as ‘Major’ last year. By comparison, around five per cent of all diesel emissions failures were classed as ‘Dangerous’, meaning the car should not be driven until the fault is rectified.

Jessica added: “Since the Volkswagen ‘dieselgate’ scandal in 2015, diesel cars have earned a bad reputation for producing harmful exhaust emissions.

“That’s not to say all diesels are bad. The latest diesel cars are equipped with emissions control systems such as particulate filters and selective catalytic reduction (AdBlue) to reduce or eliminate harmful emissions.

“What this data tells us though, is that an increasing number of relatively modern diesels are struggling to pass the MOT test as their emissions control systems face tougher scrutiny. It’s important these systems function correctly to protect the environment, but putting them right can also cost owners thousands of pounds.”

Written by:

Published on: January 29, 2021

Filled Under: Exhaust, News

Web site:

Comments are closed.